Imageable silicon-containing polymer films comprising components which impart resistance to oxygen reactive-ion-etching (O.sub.2 RIE) have utility as resist layers in bilayer lithographic processes wherein a resist pattern is transferred into underlying polymer films by O.sub.2 RIE with the top layer serving as a RIE mask during the etching process. Bilayer lithographic approaches are preferred over the standard tri-layer or multi-layer resist (MLR) processes because they require fewer operations and thus provide process simplification. The MLR processes are generally based on a three layer stack comprising an organic polymer underlayer/RIE mask/imaging layer structure in which the RIE mask may be silicon oxide, silicon nitride, silicon oxynitride, plasma deposited organosilicons or solution coated siloxane polymers including "glass resins", or silicon containing polyimides, and the imaging layer is formed from any of the standard photoresist formulations such as AZ 1350J or other positive or negative working photoresists well known in the art.
Fabrication of high density multilayer copper/polyimide interconnections in thin film technology utilizing dry-etch techniques, generally requires extended O.sub.2 RIE to etch patterns into relatively thick polymer underlayers. Commonly used underlayers in high temperature metallization processes include soluble polyimides for metal lift-off schemes and polyimide dielectric materials for insulating metal circuits.
Typical multilayer lithographic schemes in thin film fabrication are described in U.S. Pat. Nos. 4,789,648, 4,770,897, and U.S. patent application Ser. No. 07/740,760, filed Aug. 15, 1991, Attorney Docket No. FI9-91-086 the disclosure of which is incorporated herein by reference, which describes applications of low TCE polyimides as improved insulator for high conductivity metallurgical circuits in semiconductor device and packaging technologies.
Bilayer lithography offers an alternative method of patterning polyimide underlayers by dry etching and can provide significant simplification in the overall process. However, successful application of a bilayer process in the fabrication of multilayer thin film structures using polyimides requires that the top resist mask (imageable O.sub.2 RIE mask) have the following functional characteristics: high O.sub.2 etch resistance to provide high etch-rate-ratio with respect to the underlying polymer layer; no change in lithographic performance when used in conjunction with polyimide underlayers that are cast from NMP as solvent; mechanical integrity during extended O.sub.2 RIE, there should be no cracking, crazing, or image flow during image transfer; good adhesion to the underlying polymer at all levels of processing; and compatibility of the resist with the underlayer such that resist application causes no cracking or surface crazing in the underlayer. In addition to these requirements, the resist should provide defect-free films, should have good shelf-life, reproducible performance in terms of dose requirement and image resolution, and should be stable to environmental effects.